Segment and Nonregulated Business Reporting (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) subsidiaries	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of Subsidiaries | subsidiaries				5
Operating revenue		$ 86,944	$ 72,402	$ 148,056	$ 134,514
Operating expense		57,144	55,192	107,675	104,499
Operating income (loss)		29,800	17,210	40,381	30,015
Net income (loss)		16,775	7,461	20,153	12,156
Depreciation and amortization		11,187	10,202	22,370	20,361
Senior note, mortgage and other interest expense		5,469	5,618	10,904	11,270
Income tax expense (benefit) in net income		10,911	4,405	13,033	7,199
Assets		1,399,337	1,295,857	1,399,337	1,295,857	$ 1,337,325
Water Utility Services | Regulated
Segment Reporting Information [Line Items]
Operating revenue		83,746	69,011	141,887	127,898
Operating expense		54,667	52,555	102,788	99,477
Operating income (loss)		29,079	16,456	39,099	28,421
Net income (loss)		15,023	7,556	18,594	12,257
Depreciation and amortization		10,676	9,693	21,349	19,372
Senior note, mortgage and other interest expense		4,655	4,814	9,281	9,644
Income tax expense (benefit) in net income		9,705	4,457	11,977	7,275
Assets		1,314,565	1,205,819	1,314,565	1,205,819
Water Utility Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		1,542	1,588	2,746	3,035
Operating expense		1,038	1,343	1,920	2,305
Operating income (loss)		504	245	826	730
Net income (loss)		214	55	319	273
Depreciation and amortization		118	121	234	211
Senior note, mortgage and other interest expense		0	0	0	0
Income tax expense (benefit) in net income		168	93	274	275
Assets		18,976	18,611	18,976	18,611
Real Estate Services | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		1,656	1,803	3,423	3,581
Operating expense		1,021	1,003	2,053	2,027
Operating income (loss)		635	800	1,370	1,554
Net income (loss)		178	272	431	532
Depreciation and amortization		393	388	787	778
Senior note, mortgage and other interest expense		240	255	490	510
Income tax expense (benefit) in net income		107	163	248	308
Assets		64,867	67,066	64,867	67,066
All Other | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue	[1]	0	0	0	0
Operating expense	[1]	418	291	914	690
Operating income (loss)	[1]	(418)	(291)	(914)	(690)
Net income (loss)	[1]	1,360	(422)	809	(906)
Depreciation and amortization	[1]	0	0	0	0
Senior note, mortgage and other interest expense	[1]	574	549	1,133	1,116
Income tax expense (benefit) in net income	[1]	931	(308)	534	(659)
Assets	[1]	929	4,361	929	4,361
SJW Corp. | Regulated
Segment Reporting Information [Line Items]
Operating revenue		83,746	69,011	141,887	127,898
Operating expense		54,667	52,555	102,788	99,477
Operating income (loss)		29,079	16,456	39,099	28,421
Net income (loss)		15,023	7,556	18,594	12,257
Depreciation and amortization		10,676	9,693	21,349	19,372
Senior note, mortgage and other interest expense		4,655	4,814	9,281	9,644
Income tax expense (benefit) in net income		9,705	4,457	11,977	7,275
Assets		1,314,565	1,205,819	1,314,565	1,205,819
SJW Corp. | Non-tariffed
Segment Reporting Information [Line Items]
Operating revenue		3,198	3,391	6,169	6,616
Operating expense		2,477	2,637	4,887	5,022
Operating income (loss)		721	754	1,282	1,594
Net income (loss)		1,752	(95)	1,559	(101)
Depreciation and amortization		511	509	1,021	989
Senior note, mortgage and other interest expense		814	804	1,623	1,626
Income tax expense (benefit) in net income		1,206	(52)	1,056	(76)
Assets		$ 84,772	$ 90,038	$ 84,772	$ 90,038

[1] * The “All Other” category includes the accounts of SJW Corp. on a stand-alone basis and SJW Group, Inc. For the three and six months ended June 30, 2016 and 2015, SJW Group, Inc. had no revenue or expenses recorded and held no assets as of June 30, 2016.